1. Do Now: SWBAT: Apply the three principles of experimental design.
Your statistics class has 30 students. You want to call an SRS of 5 students from your class to ask where they use a computer for the online exercises. You label the students 01, 02,…, 30. You enter the table of random digits at this line:
14459    26056    31424    80371    65103    62253    22490    61181
Your SRS contains the students labeled
(a) 14, 45, 92, 60, 56.
(b) 14, 31, 03, 10, 22.
(c) 14, 03, 10, 22, 22.
(d) 14, 03, 10, 22, 06.
(e) 14, 03, 10, 22, 11.

2. Observational Study versus Experimental Study
SWBAT: Apply the three principles of experimental design.
Observational Study versus Experimental Study
Observe individuals without attempting to influence responses
Imposes some treatment on individuals to measure their responses.
* Needed For cause and effect

3. Lurking Variables versus Confounding Variables
SWBAT: Apply the three principles of experimental design.
Lurking Variables versus Confounding Variables
Outside variable that influences response variable.
two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other.

4. SWBAT: Apply the three principles of experimental design.
Example: Refer to the following setting: Does eating dinner with their families improve students’ academic performance? According to an ABC News article, “Teenagers who eat with their families at least five times a week are more likely to get better grades in school.” This finding was based on a sample survey conducted by researchers at Columbia University.
Was this an observational study or an experiment? Justify your answer.
b) What are the explanatory and response variables?
Explain clearly why such a study cannot establish a cause-and-effect relationship. Suggest a lurking variable that may be confounded with whether families eat dinner together.

5. Bad versus Good Experiments
SWBAT: Apply the three principles of experimental design.
Bad versus Good Experiments
Bad
Completely randomized design

6. 1. Control for lurking variables. Use a comparative design.
SWBAT: Apply the three principles of experimental design.
Three Principles of Experimental Design
1. Control for lurking variables. Use a comparative design.
2. Randomize assignment to ensure equal groups.
3. Replication ensures enough individuals in each group.

7. SWBAT: Apply the three principles of experimental design.
Example: Music students often don’t evaluate their own performances accurately. Can small-group discussions help? The subjects were 29 students preparing for the end-of-semester performance that is an important part of their grade. Assign 15 students to the treatment: videotape a practice performance, ask the student to evaluate it, then have the student discuss the tape with a small group of other students. The remaining 14 students form a control group who watch and evaluate their tapes alone. At the end of the semester, the discussion-group students evaluated their final performance more accurately.
Outline a completely randomized design for this experiment. Follow the model of a completely randomized design
Describe how you would carry out the random assignment. Provide enough detail that a classmate could implement your procedure.
What is the purpose of the control group in this experiment?